Cathode ray tube and the like



Aug. 13, 1940.

R. M. BOWIE CATHODE RAY TUBE AND THE LIKE Original Filed Aug. 14, 1936 4 Sheets-Sheet l 3noentor (Ittorneg Aug. 13, 1940. R. M. BOWIE CATHODE RAY TUBE AND THE LIKE Original Filed Aug. 14, 1936 4 Sheets-Sheet 2 ttorneg Aug. 13, 1940. R. M. BOWlE CATHODE RAY TUBE AND THE LIKE Original Filed Aug. 14, 1936 4 Sheets-Sheet 3 311192 tor flai Aug. 13, 1940. v R. M. BOWIE CATHODE RAY TUBE AND THE LIKE Original Filed Aug. 14, 1936 4 Sheets-Sheet 4 3nnentor (litorneg Patented Aug. 13, 1950 UNITED STATES 2,211,614 CATHODE BAY TUBE AND THE LIKE Robert M. Bowie, St.

Hygrade Sylvanla Corporation,

Marys, Pa., assignor to Salem, Mass,

a corporation of Massachusetts Original application 95,970. Divided and August 14,

1936, Serial No. this application June 24,

1937, Serial No. 150,034

17 Claims.

This invention relates to electron tubes and more particularly to tubes of the cathode ray type, such for example as are used in oscillograph systems, telautograph systems, television systems and the like.

I have found that with the ordinary structure of cathode ray tube, that is, one having an elongated neck which is located substantially coaxially of the end carrying the fluorescent screen, there is a decided tendency for the cathode beam to produce a localized blackening or darkening of the screen. This tendency is particularly marked in cathode ray tubes employing a fluorescent material containing sulfides and the like, and more especially so in the case of cathode ray tubes employing magnetic action for the coordinate deflections of the beam.

Accordingly it is one of the principal objects of the present invention to provide a cathode ray tube of novel construction wherein the tendency towards undesirable darkening of the screen is substantially avoided. I have found that this localized blackening or darkening of the fluorescent screen i'scaused by the presence of 25 negatively charged heavy particles or ions which are emitted from, or are developed at, the cathode. When such heavy particles strike the fluorescent material of the screen, some action or reaction takes place which causes the fluorescent material to decrease its luminous efliciency. Because of the relatively heavy mass of these negatively charged particles as compared with the beam electrons they are subject to very little deflecting action by the usual magnetic deflect- 35 ing means, with the result that the darkening of the screen becomes localized at or near the center thereof where it is most conspicuous. While the exact physical nature of \the blackened or darkened area is not well-known, it may consist of avery' thin coating of the metal particles, although the darkened spot is not usually visible under ordinary reflected light.

It is well-known that the trajectory of a charged particle in a constant electric field is 0 independent of charge-to-mass ratio of the particle, and this is so even if the electric fleld changes ata rate which is slow compared to the time of flight of the particle. Consequently it is practically impossible to separate heavy particles such as ions, from'electrons, merely by using electric fields. If it is assumed that the beam is non-homogeneous, that is it is composed of both heavy and light particles all of which have their origin in or at the same cathode, and that such a beam is acted upon by a magnetic field having a component perpendicular to the direction of motion of the particles, then the beam can be separated into several beams, depending upon the charge-to-mass ratios of the various particles composing the beam. If

such a magnetic fleld is applied in a region which is substantially free from electric fields, the bending of the trajectory of the various particles in the beam can be expressed mathe matically as follows:

r=radius of curvature of trajectory H=component of magnetic field strength perpendicular to beam E=potential through which the particles have fallen since leaving the cathode &=mass-t0-charge ratio I have found that it is possible to construct a cathode ray tube wherein the objectionable heavy particles are deflected or shunted before they reach the fluorescent screen by taking advantage of the different actions exerted on the particles by magnetic and electric fields.

Accordingly it is a feature of the present invention to provide a cathode ray tube with an elongated neck which is offset at an angle with respect to the axis of the screen, so that the heavy particles strike a part of the tube envelope remote from the screen or at least remote from the useful part of the screen.

'Another feature relates to a bent neck cathode ray tube having means to subject the electrons in the beam to a constant magnetic field, in addition to the usual deflecting means. As a result of this arrangement the objectionable heavy particles are shunted away from the electron beam before they strike the fluorescent screen, while the electrons in the beam are guided around the bend of the tube so that they may be subjected to the usual deflecting action.

Another feature relates to a cathode ray tube having specially arranged separate magnetic and electric fields to shunt away the objectionable heavy particles from the fluorescent screen, while allowing the electron beam to impinge upon the screen after the usual deflecting action thereon.

Another feature relates to a conventional cathode ray tube having a straight neck which is provided with separate electric and magnetic deflecting means, said means being so biased electrically that the objectionable heavy particles in the beam are diverted away from the fluorescent screen. k

A further feature relates to the novel organization, arrangement and relative location of parts which go to make up an improved cathode ray tube.

Other features and advantages not specifically enumerated will be apparent after a consideration of the following detailed descriptions and the appended claims.

In the drawings,

Fig. 1 illustrates in partial perspective a cathode ray tube embodying features of the invention.

Fig. 1a is a plan view of Fig. 1.

Fig. 2 illustrates a modified embodiment of the invention.

Fig. 3 is an enlarged detail view, of part of the electrode structure of Fig. 2.

Fig. 4 illustrates another embodiment of the invention.

Fig. 5 illustrates a still further embodiment of the invention;

Referring more particularly to Fig. 1, the oathode ray tube comprises a highly evacuated enclosing envelope consisting of a funnel shaped supported on the stem in any well-known manner. Any suitable form of contact base I may be fastened to the neck for the purpose of making electrical contact with the various electrodes of the electron gun. Preferably, although not necessarily, the envelope is of glass and is coated on its interior surface as indicated by the stippled area with a conductive material such as aquadag, except of course the screen portion 2, which is provided with any well-known fluorescent material preferably, although not necessarily; zinc sulfide or a mixture of sulfides. In the usual form of electron gun there is provided an electron emitting cathode, a control grid, a first anode and a second anode coacting to produce a focussed beam. Merely The aquadag" coating 8 may serve as the usual second anode and for this purpose a contact terminal 9 is provided therefor so that the appropriate potential may be impressed thereon. As pointed out hereinabove, the beam consists for the most part of electrons emitted by the cathode and also a certain percent of relatively heavy negatively charged particles originating at or near the cathode, and is represented in the drawings by the heavy dotted line. Because of the difference of potential between the electron gun cathode and the second anode 8, this composite beam is composed of particles having velocities given by the following equation:

i v x/Z E where,

v =velocity of a particle in the beam =potential difference between cathode and anode Z=charge-to-mass ratio of a particle Winding, It may be energized from any suitable battery I5 is so arranged that the source of steady magnetizing current represented diagrammatically by the battery l5. purpose of adjusting the intensity of magnetization a series variable resistor I6 is preferably provided. It is important that the poles of the magnet be so disposed, and the polarity of magnetization be such that the electrons in the beam are bent back along the axis of the straight portion 3 of the neck. Assuming for example that the tube is positioned so that the bent portion 4 and the straight portion 3 are disposed plane, then the magnet is so positioned that the magnetic lines of force between poles II and II are substantially horizontal, and the polarity of pole II is a consists substantially entirely of electrons and this beam can be subjected to any of the wellknown types of control. For example as shown ment under control of suitable signals. Likewise a similar set of magnets (not shown) may be provided and energized by suitable signals to impart to the electron beam a horizontal component of movement.

Instead of allowing the objectionable particles to strike the glass in Fig. 3 the electron gun comprises an electron emitting cathode 22 of known construction preferably, although not necessarily, in the form of vided with another concentric circular groove in such for example by the annular mica disc 21. Preferably the tubular member 26 is provided on its interior with a series of perforated metal diaphragms 29, 30 to assist in focusing the beam. The electron gun as described may be supported in any suitable manner from the stem 3| of the envelope.

As will be seen from Figs. 2 and 3, the tubular anode 26 is formed with a bend 32 conforming to the bend 33 in the neck of the envelope, and the greater part of the inner surface of the envelope is provided with a conductive coating 8 of aquadag or other suitable conductive material forming the second anode. The electrons which leave the cathode 22 passthroughtheaperture 24 in the end of grid 23 and thence accelerated through the perforation 34 by the first anode potential. The composite beam 35 constituted of electrons and negative ions then enters the region adjacent the bend 32 where are situated magnetic poles similar to the poles |2 shown in Fig. 1. With the particular position of the tube as shown in Fig. 3, these poles are positioned so as to produce a magnetic field perpendicular to the paper. The intensity of magnetization of these poles is adjusted as described so that the electrons in the beam are deflected to pass through the perforation 36 and thence along the path designated by the dotted line 31 axially of the neck 3. The negative ions however are scarcely deflected by the magnet poles and continue along the path 38, striking the wall of tube 26. Thus the beam that emerges from the electron gun, emerges axially thereof and is a homogeneous electron beam substantially free from negative ions or other objectionable heavy negatively charged particles.

Instead of providing a bend in the neck portion intermediate its ends as in Figs. 1 and 2, the neck portion may be straight and may be joined to the funnel shaped part of the envelope at an angle to the axis of the latter. Thus as shown in Fig. 4 the neck 39 is straight throughout substantially its entire length except for the region where it joins the funnel shaped part 40 of the envelope. In other Words, the neck is joined to the part 40 so that the axis of the neck is at a predetermined angle with respect to the axis of the part 40. As in the previous embodiments the inside surface of the envelope is provided with a conductive coating 4| and the substantially flat end 42 is provided on its inner surface with a suitable fluorescent coating. An electron gun 43 of any well-known construction is mounted in the neck 39 and emits a substantially parallel beam 44 of electrons and negative ions which travel along the axis of the neck 3. Mounted outside the tube and preferably adjacent the region where the neck joins the part 40 of the envelope, are two electro-magnets 45,46 so disposed that their respective fields are in mutually perpendicular directions. The magnet 45 is used to deflect the beam from right to left as indicated by the full line arrows on the screen, while the magnet 46 isused to deflect the beam vertically as represented by the dotted arrows. In addition to serving as the vertical deflecting means, the magnet 46 also serves to segregate the electrons from the negative ions or other negatively charged objectionable particles. For this purpose the winding 41 is connected to a source of steady biasing potential such for example as the battery 48 in series with a variable resistor 49. Winding 41 is also arranged to be connected to the terminals 50, leading to a suitable source of deflecting signal current, and preferably the signal current is segregated from the biasing circuit by means of the condenser 52 and choke coil 53. Thus the magnet 46 is. energized by a steady direct current for biasing and having superimposed thereon the variable deflecting signal current. In accordance with the invention the steady biasing current is adjusted to such a magnitude that the electron beam is normally deflected along the dot-dash line 54 and strikes the center of the screen 42, when no deflecting signal is applied to terminals ill, 5|. The excitation of winding 41 therefore effects the vertical deflection of the electron beam, and the maximum magnitude of the vertical deflecting signal is preferably chosen so that the electron beam never strikes the marginal portion of the screen 42. As pointed out hereinabove, the magnet 46 exerts very little deflecting action on the negative ions or negatively charged heavy particles in the beam with the result that these ions and particles follow substantially their original path as indicated by the" dotted line 55 thus striking the screen only at its marginal area. It will be understood of course that the magnet 45 for effecting the horizontal movement of the electron beam is provided with a winding 56 connected to terminals 51, 58 leading to a suitable source of signal deflecting current. If desired the horizontal deflection of the electron beam may be effected by electrostatic reflecting electrodes as is well understood in the art, instead of the magnet 45.

Referring to Fig. 5, there is shown a method of segregating the negative ions or particles from the electron beam, in a cathode ray tube of the straight neck type. In this embodiment the cathode ray tube is formed with a straight neck 60 which is formed co-axially with the funnel shaped portion 6|. The electron gun 62 emits a beam 63 of negative ions and electrons the beam passing between the electrically charged deflecting plates 64, 65 and also between the poles of electro-magnet 66, the said poles being disposed so as to produce a magnetic field therebetween which is perpendicular to the field between plates 64, 65. The winding 61 of magnet 66 is connected to a source of steady current represented by battery 68 in series with an adjustable resistor 69. Likewise the plates 64, 65 are connected across a source of steady potential represented by battery and potentiometer 1|. Preferably, although not necessarily, the conductive coating on the interior of the envelope is connected to the mid-point of the potentiometer 1|. I have found that by suitably adjusting the intensity of the magnetic field between the poles of magnet 66, with respect to the electric field between plates 64, 65 it is possible to have the electrons in the beam continue in a substantially straight line along the axis of the tube and thence through the perforation 12 in the metal diaphragm 13 to the center of the screen 14, while the heavy particles or ions in the beam are deflected along the path 15. Instead of adjusting the relative magnetic and electric field strengths so as to cause the heavy particles to strike the diaphragm as shown, it is possible to adjust these field strengths so that the heavy particles strike the neck of the tube in which event the diaphragm 13 may be omitted. The beam that reaches the screen therefore consists substantially entirely of electrons and it can be deflected in a vertical direction, a horizontal direction, or both, by suitable deflecting means either in the form of electro-magnets or in the form of electrostatic deflecting plates similar to plates 64, 65 it being understood that these deflecting members or electrodes are preferably positioned at the region of the tube indicated schematically by the magnets 16, 11.

While certain specific embodiments and ma terials have been disclosed it will be understood that the invention is not limited thereto and thatvarious changes and modifications may be made without departing from the spirit and scope of the invention. Furthermore it is understood that the invention is not limited by the theories set forth as to-the cause of the darkening of the cathode ray tube screen. Furthermore while the invention is disclosed in connection with an'all glass cathode ray tube envelope, it will be understood that the invention is capable of application to cathode ray tubes wherein the funnel shaped part is of metal rather than of metal coated with a conductive material.

This application is a division of application Serial No. 95,970, filed August 14, 1936.

What I claim is:

1. In combination, a cathode-ray tube having an evacuated envelope with an electron gun 'of the thermionic emitting cathode type and a screen to be scanned by the electron beam from said gun which screen is subject to permanent localized discoloration by bombardment with heavy particles or ions in said beam, said gun arranged to emit a beam of electrons having substantially parallel paths and normally tending to follow a substantially straight line toward said screen, control means to move said beam in a desired scanning path over said screen, means to energize said control means by signals, and means separate from said control means for segregating the electrons in the beam from the said heavy particles or ions before the latter reach said screen, the last-mentioned means including a field producing device for causing the beam to follow a curved path towards said screen and a source of biasing potential connected to said device for adjusting the curvature of said beam.

2. In combination, a cathode-ray tube having an evacuated envelope with an electron gun of the thermionic emitting cathode type and a screen to be scanned by an electron beam from said gun which screen is subject to permanent localized discoloration by bombardment with heavy particles or ions in said beam, said gun including an electrode system for accelerating the particles of the beam towards said screen, and means to divert undesirable heavy negative particles or ions from the electrons before said particles or ions reach the useful scanning area of said screen, the last-mentioned means including a magnet for producing a magnetic field transverse to said beam, and an arrangement for producing an electric field also transverse to said beam and substantially perpendicular to said magnetic field, and potential adjusting means connected respectively to said magnet and to said electric field producing arrangements to adjust said fields to predetermined relative intensities.

3. The combination according to claim 2 in which the magnet and the said electric field producing arrangement are located to act upon the beam at substantially the same region, and separate signal-controlled means are provided to oscillate the beam after it has been acted upon by said perpendicular fields.

4. In combination, a cathode-ray tube having an evacuated envelope with a constricted neck joined to a funnel-shaped portion, and with a screen scanned by an electron beam the screen being subject to permanent localized discoloration when bombarded by heavy particles or ions in said beam, an electron gun including a thermionic cathode and a pair of anodes one of which is a final high voltage anode, said gun being mounted in said neck and arranged normally to emit a beamof electrons emerging from said second anode at an angle to the axis of said funnel portion, means between said gun and. screen to divert said heavy particles or ions away from the electrons before said particles or ions reach said screen, the last-mentioned means infield means, separate beam deflecting means ac't- Y ing on said beam after passage through said bailie, and means to energize said separate deflecting means by variable potential signals.

5. In combination, a cathode-ray tube having an evacuated envelope with an electron gun of the electrostatically focussed thermionic emitting cathode type, said tube having a fluorescent screen which is subject to localized deterioration when bombarded by heavy particles or ions, a magnet between the gun and screen for producing a magnetic field transverse to focussed beam, said field diverting said heavy particles or ions which tend to move in the same direction away from said electrons before said particles or ions reach the useful scanning area of said screen, an

adjustable source of steady biasing potential connected to said magnet to control the divergence of said ions or particles with respect to the electrons, separate electron beam deflecting means, and means to energize said separate deflecting means by variable potential signals.

6. In combination, a cathode-ray tube with a screen which is subject to localized deterioration when bombarded by heavy particles or ions, said tube having an evacuated envelope with an electron gun of the electrostatically focussed thermionic beam type, said gun including a hot electron-emitting cathode and an electrode system for focussing andaccelerating said electrons towards said screen, said gun being positioned so that normally the beam after leaving the gun does not impinge on any useful scanning area of said screen, means to bend the electron beam toward the useful scanning area of the screen while allowing the heavy particles or ions to be diverted from said useful area, the last-mentioned means including an electromagnet between the gun and screen and a source of steady beam biasing potential connected to said electromagnet to effect said bending of the electron beam.

7. The combination according to claim 6 in which said electromagnet is also connected to a source of variable potential scanning signals.

8. The combination according to claim 6 in which separate means are provided for producing a variable beam deflecting scanning field substantially at right angles to th field produced by said electromagnet.

9. The combination according to claim 6 in which said electrode system includes a first anode and a final high voltage anode, and the said means to bend the electron beam is located between said final anode and said screen.

10. The combination according to claim 1 in which said means for causing the beam to follow a curved path is located between the gun and screen to act on the electrons after they have attained substantially their final velocity.

11. The method of preventing permanent lo- I calized deterioration, by heavy ions or particles, of the screen of an evacuated cathode-ray tube of the type wherein the electron gun is of the electrostatic focussed kind and has a second high potential anode located normally to direct the beam away from the useful scanning area of the beam after it leaves the gun to at least one magnetic deflecting field transverse to the beam,'proportioning the intensity of the said transverse field and arranging its direction so that only the electrons in the beam strike the useful scanning area of the screen while allowing heavy particles or ions in'the beam to be diverted away from said screen, and subjecting said beam to another deflecting field under control of variable potential deflecting signals.

12. The method of preventing permanent lo- 'calized deterioration by negative ions of the screen of an evacuated cathode-ray tube of the type employing an electrostatically focussed electron gun', which method comprises normally directing the electron beam after leaving the gun away from a useful section of the screen, subjecting the focused beam to a transverse magnetic steady biasing field to cause only the elec-v trons in the beam to strike the useful area of the screen, and superimposing on said biasing field a variable field controlled by scanning signals.

13. The combination of a cathode-ray tube having an electron gun with a thermionic emitting cathode at one end and a fluorescent screen at the other end, a pair of plates between which the electron beam passes, an electromagnet havbeing relatively adjusted so that the beam which strikes the screen is a substantially homogeneous electron beam and undesired heavy negative particles originally moving in the direction of the beam electrons are diverted away from the useful part of said screen, and separate means energized by scanning signal currents to subject the beam electrons to scanning movement.

14. The combination according to claim 13 in which a perforated diaphragm is provided between the scanning control means and said plates to allow only the beam electrons to pass to said screen.

l5. The method of preventing negative ions from striking the screen of a highly evacuated cathode-ray tube having the electron gun directed toward the-screen and having at least one pair of deflector fleld producing means, which method consists in applying to one of the field producing means a bias potential adequate under normal working conditions to direct the ions off the screen, and applying a potential to the other field producing means to nullify the deflection efiect of said bias upon the electrons thereby to direct them on to the screen.

16. The method of preventing negative ions from striking the screen of a highly evacuated cathode-ray tube having the electron gun directed toward the screen and having at least one pair of electrostatic deflector plates, which method consists in applying between a pair of electrostatic deflector plates a bias potential difference adequate under normal working condi-' tions to direct the ions off the screen, and applying a magnetic deflecting field to nullify the deflection eifect of said bias upon the electrons and thereby to direct them on to the screen.

1'7. The method according to claim 16 in which the said bias potential is superimposed upon a- 

